A light emitting diode (LED) is a semiconductor light-emitting device, which is widely applied in display or lighting field like indicator light and display screen for its environmental performance, high luminance, low power consumption, long service life, low working voltage and easy integration. White light LED has become the fourth-generation new lighting source following incandescent lamp, fluorescent lamp and high intensity discharge lamp (e.g., HPSL).
In the past few years, thanks to material and technology breakthroughs, luminance of white light LED is greatly improved and its lighting effect is completely outperformed over the fluorescent lamp. However, high initial purchase price of the LED—about two times of that of the fluorescent lamp—has restricted its popular application in lighting. Only after long-time service, comprehensive cost of the LED is lower than that of the fluorescent lamp when power-saving cost and replacement cost are considered. And power-saving effect of LED is not recognized by the public for its actual service time is usually shorter than theoretical time. In particular, during long-time service of high-power chip, aging electric leakage always restricts long time service of the LED.